diff --git a/clippy_lints/src/consts.rs b/clippy_lints/src/consts.rs
index eadadaa1932a..aeb82a0c8cd3 100644
--- a/clippy_lints/src/consts.rs
+++ b/clippy_lints/src/consts.rs
@@ -152,7 +152,7 @@ impl Constant {
 }
 
 /// Parses a `LitKind` to a `Constant`.
-pub fn lit_to_constant(lit: &LitKind, ty: Ty<'_>) -> Constant {
+pub fn lit_to_constant(lit: &LitKind, ty: Option<Ty<'_>>) -> Constant {
     use syntax::ast::*;
 
     match *lit {
@@ -161,7 +161,9 @@ pub fn lit_to_constant(lit: &LitKind, ty: Ty<'_>) -> Constant {
         LitKind::ByteStr(ref s) => Constant::Binary(Lrc::clone(s)),
         LitKind::Char(c) => Constant::Char(c),
         LitKind::Int(n, _) => Constant::Int(n),
-        LitKind::Float(ref is, _) | LitKind::FloatUnsuffixed(ref is) => match ty.kind {
+        LitKind::Float(ref is, FloatTy::F32) => Constant::F32(is.as_str().parse().unwrap()),
+        LitKind::Float(ref is, FloatTy::F64) => Constant::F64(is.as_str().parse().unwrap()),
+        LitKind::FloatUnsuffixed(ref is) => match ty.expect("type of float is known").kind {
             ty::Float(FloatTy::F32) => Constant::F32(is.as_str().parse().unwrap()),
             ty::Float(FloatTy::F64) => Constant::F64(is.as_str().parse().unwrap()),
             _ => bug!(),
@@ -225,7 +227,7 @@ impl<'c, 'cc> ConstEvalLateContext<'c, 'cc> {
         match e.kind {
             ExprKind::Path(ref qpath) => self.fetch_path(qpath, e.hir_id),
             ExprKind::Block(ref block, _) => self.block(block),
-            ExprKind::Lit(ref lit) => Some(lit_to_constant(&lit.node, self.tables.expr_ty(e))),
+            ExprKind::Lit(ref lit) => Some(lit_to_constant(&lit.node, self.tables.expr_ty_opt(e))),
             ExprKind::Array(ref vec) => self.multi(vec).map(Constant::Vec),
             ExprKind::Tup(ref tup) => self.multi(tup).map(Constant::Tuple),
             ExprKind::Repeat(ref value, _) => {
diff --git a/clippy_lints/src/neg_multiply.rs b/clippy_lints/src/neg_multiply.rs
index aec0664a29b2..3ef3ee36c3f0 100644
--- a/clippy_lints/src/neg_multiply.rs
+++ b/clippy_lints/src/neg_multiply.rs
@@ -44,7 +44,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NegMultiply {
 fn check_mul(cx: &LateContext<'_, '_>, span: Span, lit: &Expr, exp: &Expr) {
     if_chain! {
         if let ExprKind::Lit(ref l) = lit.kind;
-        if let Constant::Int(1) = consts::lit_to_constant(&l.node, cx.tables.expr_ty(lit));
+        if let Constant::Int(1) = consts::lit_to_constant(&l.node, cx.tables.expr_ty_opt(lit));
         if cx.tables.expr_ty(exp).is_integral();
         then {
             span_lint(cx, NEG_MULTIPLY, span, "Negation by multiplying with -1");